Treating the exhaust gases from an internal combustion engine, e.g. a spark-ignition or diesel engine, by an exhaust gas aftertreatment device arranged in the exhaust tract in order to reduce pollutant emissions is a widely known practice. In this case, the efficiency or effectiveness of the exhaust gas aftertreatment device is affected by the temperature level prevailing in the exhaust gas aftertreatment device and by the fuel/air ratio used in combustion in the internal combustion engine.
Transient engine operating conditions, such as operator-induced sudden demand for torque, can result in temperature fluctuations that affect operation of downstream exhaust aftertreatment devices. For example, a selective catalyst reduction (SCR) system and a lean NOx trap (LNT) may release ammonia and NOx, respectively, when engine exhaust temperature exceeds a threshold temperature for a short period of time. Release of such compounds may negatively affect the quality of the environment, and may reduce the catalytic efficiency of the aftertreatment device.
The inventors herein recognize the above issues and have provided an exhaust system to at least partly address the issues. In one example embodiment, an exhaust system for an internal combustion engine comprises an exhaust line, at least one exhaust gas aftertreatment device arranged in the exhaust line, and a heat source and a heat sink arranged in separate branches of the exhaust line upstream of the exhaust gas aftertreatment device. An exhaust gas flow rate through each respective separate exhaust branch may be controlled by at least one flow control device.
In this way, the exhaust system for an internal combustion engine may exhibit a considerably reduced ammonia and/or nitrogen oxide slip or essentially no slip at all in an SCR catalytic converter or a NOx storage catalytic converter during non-steady-state operation of the internal combustion engine, e.g. in the event of an abrupt change in the exhaust gas temperature owing to a jump in the load on the internal combustion engine, and thus allows optimum and effective operation of the exhaust system and/or of the exhaust gas aftertreatment device in terms of exhaust gas cleaning or conversion performance.
It should be pointed out that the features presented individually in the claims can be combined in any technically sensible manner and give rise to further embodiments of the disclosure. The description further characterizes and specifies the disclosure, especially in conjunction with the figures.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.